DIFFERENTIAL EXPRESSION AND MODIFICATION OF NEUROFILAMENT TRIPLET PROTEINS DURING CAT CEREBELLAR DEVELOPMENT

Neurofilament (NF) proteins consist of three subunits of different mol ecular weights defined as NF-H, NF-M, and NF-L. They are typical struc tures of the neuronal cytoskeleton. Their immunocytochemical distribut ion during postnatal development of cat cerebellum was studied with se veral monoclonal and polyclonal antibodies against phosphorylated or u nmodified sites. Expression and distribution of the triplet neurofilam ent proteins changed with maturation. Afferent messy and climbing fibe rs in the medullary layer contained NF-M and NF-L already at birth, wh ereas NF-H appeared later. Within the first three postnatal weeks, all three subunits appeared in messy and climbing fibers in the internal granular and molecular layers and in the axons of Purkinje cells. Axon s of local circuit neurons such as basket cells expressed these protei ns at the end of the first month, whereas parallel fibers expressed th em last, at the beginning of the third postnatal month. Differential l ocalization was especially observed for NF-H. Depending on phosphoryla tion, NF-K proteins were found in different axon types in climbing, me ssy, and basket fibers or additionally in parallel fibers. A nonphosph orylated NF-H subunit was exclusively located in some Purkinje cells a t early developmental stages and in some smaller interneurons later. A novel finding is the presence of a phosphorylation site in the NF-H s ubunit that is localized in dendrites of Purkinje cells but not in axo ns. Expression and phosphorylation of the NF-H subunit, especially, is cell-type specific and possibly involved in the adult-type stabilizat ion of the axonal and dendritic cytoskeleton. (C) 1996 Wiley-Liss, Inc .